This invention relates to methods and means of reducing noise and undesired signals in a radio receiver and more particularly for reducing an interfering signal among the Loran beacon signals received by a Loran receiver, by rejecting the interfering signal and compensating for any distortion that occurs as a result of the rejection.
One type of interference in a Loran-C receiver takes the form of one or more narrow band signals at the edge of the band of received beacon signals (90 to 110 KHz). These interfering signals may come from other beacons that transmit just outside of the Loran-C band and, although they are outside the band, they are relatively very high peak power and will interfere with the reception of the desired beacon signals. Heretofore, some efforts have been made to reject these narrow band undesired signals by providing a reject filter in the path of the received signals in the Loran receiver, that includes manually variable capacitor controlled by the Loran receiver operator. This system can be used effectively, but it does require the continual attention of the human operator, and so it is not automatic. It is one object of the present invention to provide a method and means for automatically locating and rejecting undesired narrow band signals in a Loran-C receiver so that the rejection occurs automatically without requiring the attention of an operator.